Linda,
My guess is a pinhole leak in the combustion tube - you can check by
bypassing it, or just change it anyway.


At 10:04 AM 1/3/2002 -0700, you wrote:
>We are using the Europa ANCA-SL 20/20 in our lab, and I am seeing a higher
>than normal signal for nitrogen in beam one.   It is normally around
>5e-10, but now it is 1.8e-9.
>
>It was fine two weeks ago, and I ran several samples on the SL with very
>good results.   The instrument was placed into standby mode on December
>22, and our lab was closed until January 2.   I replaced the quartz liner
>in the combustion tube and allowed the system to purge before opening the
>isolation valve.    I also baked out the GC column for 4 hours at
>120C.   Today I am still receiving a high signal.   I could not detect any
>leaks, and the tuning parameters are good.
>
>Any suggestions?
>
>
>Linda Osborne
>Arizona State University

David Harris
UC Davis Stable Isotope Facility
http://stableisotopefacility.ucdavis.edu
phone 530 754 7517
fax 530 752 4361